The Wireless Application Protocol (WAP) is designed to work on any existing wireless service, using such standards as SMS. SMS, or Short Message Service, is a text message service that enables short messages, usually no more than a few hundred characters in length, to be sent to and transmitted from a wireless telephone or other wireless devices. SMS appeared on the wireless scene in 1991 in Europe. The European standard for digital wireless, now known as the Global System for Mobile Communications (GSM), included short messaging services from the outset. In North America, SMS is provided on digital wireless networks based on GSM, code division multiple access (CDMA), or time division multiple access (TDMA) standards.
Unlike paging, short messages are stored and forwarded in SMS centers and the messages travel over the system's control channel, which is separate and apart from the voice channel.